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Blecha, Andrea M.1
(1) Colorado School of Mines, Golden, CO

ABSTRACT: Fluvial System Response to a Climate Aberration- Characterizing the Paleocene/Eocene Thermal Maximum in the Wasatch Formation, Western Colorado

The concurrent increase in sand deposition and a climatic aberration within the Wasatch Formation promotes a link between climate and discharge in this fluvial system. In previous investigations of similar terrestrial strata, the Paleocene/Eocene boundary corresponds to a mean annual temperature increase of approximately 10°C, resulting in a drier and more seasonal climate. Pollen data constrains this boundary to the Molina Member of the Wasatch Formation, a high net-to-gross unit conformably bounded by the floodplain muds and isolated channels of the Atwell Gulch and Shire Members.
The Molina is characterized by a dramatic expansion of sand deposition. Internally channelized sandstone sheets, composed of mainly horizontal laminations, extend in excess of 100 kilometers across the floodplain. The aerial extent of this unit records a significant increase in sandstone volume, corresponding to either an increase in discharge and climate change or increase in sediment supply related to tectonic movements. Our hypothesis that factors besides tectonics are influencing the system is supported by the sharp contrast between the sand and underlying paleosol sequences, the lateral extensiveness of the unit, and the lack of paleoflow and provenance data implying a newly exposed sediment source.
To determine the stratigraphic position of this climatic event additional palynology, relative CO2 changes through leaf stomata density, and mammalian zonation will be utilized. Facies including variegated paleosols, paludal mudstones, and isolated coal seams above and below the Molina provide ample material for analysis. By bracketing the Paleocene/Eocene boundary, we predict the increase in net-to-gross coincides with this climatic aberration.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.